I'm on the fence about this. My trainer taught her hanoverian to rear on command. He's a very energetic person and while a student was on the mare, the trainer accidently gave the cue (which was lifting her hands up) while trying to explain something to the rider.
Needless to say, it took her FOREVER to break the mare from rearing. Very smart horse with a great memory. It was just dangerous.
The horse looks balanced, and sure it's a great trick and all that. But I would NEVER teach it to a barrel horse. EVER. Barrel horses are a different breed. They get hyped up and teaching a horse to rear, is just going to cause problems in the future. He's a great horse now, but he's young and hasn't been run very much. What happens in 2 years when he is a psycho horse and you can't get him into the gate and since he's been taught to rear, he thinks it's okay, and does it.
I had a pony that was a "hopper" and "semi-rearer" He didn't go high, but it was super annoying. When he got hyped up at the gate, we bounced into the arena a lot of the time until I was able to break him of the very naughty habit.
Rearing is one of the tricks that I never taught my horse. He knows how to shake, bow and lie down on command and that's all the further I ever wanted him to perform because of the story my trainer told me.
"The greatest pleasure of a dog is that you may make a fool of yourself with
him and not only will he not scold you, but he will make a fool of himself too."